For processes involving interactions between particulate solids and a gas phase, fluidizing the solids with the gas phase is often a useful approach to accomplish processing objectives. Many commercial processes employ fluidized bed technology in a variety of ways including, for example, for performing gas-solids reactions, for polymerizations, chemical depositions, calcining, drying, for activation of catalysts and for other processes. Many of these processes employ dense phase handling, especially solids fluidization, because of the favorable performance characteristics fluidized solids procedures can provide with respect to heat transfer, mass transfer, reaction kinetics, physical handling, physical size, particulate solids transport and/or other factors. These factors can often provide cost-effective processing yielding high quality products.
A variety of fluidized methods and apparatus are known for processing fluidized solids. Some of these are shown in FIGS. 1-3 of the accompanying drawings which are described in detail below. For example, a continuous processing method can be carried out by continuously supplying particulate solids into an upper portion of a fluidized bed processing vessel, discharging the particulate solids from the other side of the processing vessel and supplying fluidizing gas through the bottom of the vessel to cause the particulate solids to fluidize.
Another processing apparatus comprises a number of stage vessels connected together in series by transfer tunnels extending between each stage vessel and its neighbor. Each stage vessel receives its own supply of fluidizing gas to generate a fluidized bed of the particulate solids. The solids product to be processed can be fed continuously into the first stage vessel at a desired constant volumetric production rate. The solid particle populations traveling through the system have a residence time which depends upon the shape and size of the individual stages as well as the volumetric flow rate.
In many fluidized bed processes, the residence time of the solid particles in the system is important and desirably should be predictable and uniform for all solids particles traversing the system. However, in practice, these goals may be difficult or impossible to meet owing to bypassing and holdback phenomena which cause some solid particles to follow shorter than average paths through the system, and other solid particles to follow longer than average paths through the system. Consequently, there is usually a significant variation in residence times of solid particles processed.
Accordingly, it would be desirable to provide methods and systems for fluidized bed continuous processing of particulate solids which can better control the distribution of the residence times of particles processed.
The foregoing description of background art may include insights, discoveries, understandings or disclosures, or associations together of disclosures, that were not known to the relevant art prior to the present invention but which were provided by the invention. Some such contributions of the invention may have been specifically pointed out herein, whereas other such contributions of the invention will be apparent from their context. Merely because a document may have been cited here, no admission is made that the field of the document, which may be quite different from that of the invention, is analogous to the field or fields of the present invention.